Ceramic coatings are described in U.S. Pat. Nos. 4,248,940 to Goward et al, 4,321,311 to Strangman and 4,676,994 to Demaray. Exemplary ceramics include zirconia stabilized by magnesia, ceria or yttria. Other types of ceramic coatings are also known, and include, for example, Al.sub.2 O.sub.3 and MgO, TiN and Si.sub.3 N.sub.4, and SiC. Ceramic coatings may be used in combination with a metallic coating layer, as discussed in the aforementioned patents, or they may be applied directly to the substrate surface.
Goward applies ceramic coatings by plasma spray techniques, while Strangman and Demaray apply ceramic coatings by EB-PVD techniques. Several investigators have described methods for introducing oxygen into the coating chamber during the EB-PVD of ceramic coatings. See, for example, Demaray et al. in the Proceedings of the Second Conference on Advanced Materials for Alternative Fuel-Capable Heat Engines, Aug. 1981.
While the thermal barrier coatings applied using the aforementioned apparatus and techniques have shown some utility in various industries, further improvements are sought for various applications. The present invention satisfies these needs.